1. Field of the Invention
This invention generally relates to an electro-magnetic interference protection circuit and a method, and more particularly toan electro-magnetic interference protection circuit and a method for a clock buffer.
2. Description of Related Art
As the technology advances, Internet becomes one of the most important resources for people to obtain knowledge and is a powerful tool for commercial transactions. Modem has been used in personal computers for Internet connection. Today, high speed Internet solutions such as ADSL products are widely used for better quality. In those communication devices, the transceiver ICs are driven by clock signals that are distributed from clock buffers. Hence, how to protect the clock buffers from electro-magnetic interference (“EMI”) is an important issue.
Conventionally, a ferrite bead is serially connected to the power source of the clock buffer for EMI protection. How ever, because of its inductor characteristic, the ferrite bead also affects the waveform of the clock signal. FIG. 1 is a timing diagram of the input clock signal clk-in and the output clock signal clk-out when the ferrite bead is serially connected to the power source of the clock buffer. As shown in FIG.1, the waveform of the output clock signal clk-out is affected by the ferrite bead. Hence, the communication devices cannot work properly because the highest voltage level and the lowest voltage level of the output clock signal clk-out are too close to be determined. Although the ferrite bead may protect the clock buffer from EMI, it affects the output clock signal of the clock buffer. Therefore, a solution for EMI protection without affecting the output clock signal of the clock buffer is needed.